In the WHO MDT regimen for multibacillary leprosy, which drug is used primarily for its bacteriostatic action against Mycobacterium leprae and is also used for monitoring therapeutic response?

Explanation

## Dapsone in MDT for Multibacillary Leprosy **Key Point:** Dapsone is the drug in the WHO MDT regimen for multibacillary leprosy that is **primarily bacteriostatic** against *Mycobacterium leprae* and is classically used for **monitoring therapeutic response** — particularly through dapsone sensitivity testing and assessment of adherence via urine tests (spot urine dapsone test). ### Role of Dapsone in MB MDT | Feature | Details | |---------|----------| | **Mechanism** | Bacteriostatic — inhibits dihydropteroate synthase (DHPS), blocking folate synthesis | | **Dose** | 100 mg daily (unsupervised) | | **Monitoring use** | Urine dapsone test (Cragg's test) confirms drug ingestion; dapsone sensitivity testing monitors for resistance | | **Resistance monitoring** | Mouse footpad inoculation used to detect dapsone-resistant strains | | **Side effects** | Haemolytic anaemia (especially in G6PD deficiency), methaemoglobinaemia, agranulocytosis | ### Why Dapsone, Not the Others? **High-Yield:** - **Rifampicin** is the most potent **bactericidal** agent in the MDT regimen; it kills bacilli rapidly within days. It is NOT primarily bacteriostatic. - **Dapsone** is the classic **bacteriostatic** drug in leprosy treatment and has historically been the backbone of leprosy monitoring — dapsone levels in urine (Cragg's test) are used to assess patient compliance and therapeutic response. - **Clofazimine** has a combined bacteriostatic and anti-inflammatory action; while slit-skin smear (SSS) reduction monitors overall MDT response, clofazimine is not specifically singled out as the "monitoring drug." - **Ofloxacin** is a second-line/alternative drug, not part of standard WHO MB MDT. ### Clinical Pearl Per Park's Textbook of Preventive and Social Medicine and standard leprosy guidelines, **dapsone** is the drug whose bacteriostatic action is primary and whose urinary excretion is used to monitor patient compliance and therapeutic response. The **Bacillary Index (BI)** on slit-skin smear monitors overall MDT efficacy, but dapsone-specific monitoring (Cragg's urine test, sensitivity testing) is a well-established direct_recall fact. **Mnemonic:** **D**apsone = **D**etectable in urine → **D**rug monitoring tool in leprosy. *Reference: Park's Textbook of Preventive and Social Medicine, 26th edition; WHO MDT Guidelines for Leprosy.*